Toning-bath for photographic silver-prints.



ing selenium,

UNITED STATES PATENT OFFICE.

PAUL

REHLILNDER, OF CHARLOTTENBURG, GERMANY, ASSIGNOR TO CHEMISCHE FABRIK AUFACTIEN (VORM. E.| SCHERING),

OF BERLIN, GERMANY. I

TUNING-BATH FORPHOTOGRAPHIC SILVER-PRINTS.

No Drawing.

, To all whom it may concern:

Be it known that I, PAUL REHLANDER, doctor of philosophy, chemist,citizen of the German Empire, residing at Charlottenburg, near Berlin,German Empire, have invented a new and useful Improvement in Toning-Baths for Photographic Silver-Prints, of which the following is aspecification.

It has already been proposed to. employ selenium dissolved in an alkalisulfid solution for toning photographic prints. Such solutions however,especially when dilute, rapidly deteriorate as they easily becomeoxidized by the atmosphere. Moreover the white portions of a print'turnbrownish so that the riot has to be after-treated in a bisulfite Bath.These baths are strongly alkaline and therefore afiect the hands and thepaper. Further it is only possible to obtain one tone of brown.

According to this invention I employ for.

toning silver' prints a salt of an acid containfor example a seleniumsulfate compound. 'The solutions of such salts are neutral, very stablein the presence of an alkali sulfite afld in the atmosphere.

Very dilute solutions may be employed as a solution'coiitaining even1/20% of selenium'conimences-totone. The white portions of a print arenot discolored so no after-treatment with bisulfite is necessary.

One great advantage in the use oftsuch baths is that they, are-employedin exactly the same manner as the gold and platinum solutions habituallyused and good tones of different shades can be obtained.

a Fem/pier. 1. 100 grams of sodium thiosulfate, 1.5

sulfate.-

prints, acid, substantially as described.

Specification of Letters Patent. Patented J 11116 10, 1913, Applicationfiled February 12, 1913. Serial No. 747,949. T

grams sodium selenium sulfate and 13 grams sodium sulfite sicc. aredissolved in one liter of Water. The developed and fixed silver print iswell washed and immersed in such bath for three to ten minutes accordingto the quality of the print and the tone it is desired to obtain. Thetone changes from a pure black, according to the developer employed,into a brownish or into a violet-blue tone and finally into a red one.

2. 1 gram of potassium sulfite and 1 gram of sodium selenium sulfate aredissolved in a,. l]i3tle water and added to a solution of'5 grams ofpotassium bisulfite in 30 cubic centimeters water the mixture beingheated to boiling. The solution contains mainly the potassium salt ofthe selenium trithioacid and a small quantity of potassium selenium areadded to 200 cubic centimeters of a 20% solution of sodium thiosulfate.Such bath gives the same tone and has similar richness as the firstnamed bath.

I' claim as my invention:

1. A toning bath for photographic silver prints, containing a salt of anacid which 10 cubic centimeters of such solution contains selenium,substantially as described.

'2. A toning bath for. photographic silver containing a salt of selenosulfuric In testimonywhereof I have hereunto set my signature in thepresence oftwo subscribing Witnesses.

PAUL REHLANDER.

Witnesses:

WOLDEMAR HAUPT, HENRY HAsrER.

